The present invention relates to stylus input, notepad computer systems and personal communication devices, and more particularly to an apparatus for shielding RFI/EMI fields for stylus input notepad computer systems and personal communication devices.
Notepad computer systems are computer systems where the operator manually `writes` onto a display screen using a stylus. Personal communication devices are notepad computers with an electromagnetic radiation link to another device such as a cellular telephone channel or a radio computer LAN. As the operator `writes`, the positions of the stylus are sensed by a digitizer. The digitizer converts the position information to graphic data that are transferred to the graphic processing portion of the notepad computer system. The graphic processing portion converts the graphic data into pixel data and displays the pixel data on a liquid crystal display (LCD) panel or other similar device. Thus, the `writing` that the operator does with the stylus can be stored and/or displayed on the notepad computer system.
The digitizer uses an electromagnetic field to sense the various positions of the stylus as the operator `writes`. The electromagnetic field that is transmitted from the digitizer to the stylus that the operator holds is partially absorbed and partially reflected by the stylus. Of the part that is absorbed by the stylus, most of it is either radiated or transmitted to the operator who then radiates and conducts this electromagnetic field into the surrounding environment. Once the electromagnetic field leaves the stylus and is either radiated or transmitted to the operator, it ceases to be a useful field and changes into a radio frequency interference/electromagnetic interference (RFI/EMI) field. As an RFI/EMI field, this field is subject to regulation by national agencies, such as the Federal Communications Commission in the United States. These agencies typically require that RFI/EMI fields emitted by equipment, such as a notepad computer, be limited to levels that will not affect other equipment.
RFI/EMI fields may also be transmitted from the digitizer directly to the operator if the operator touches or almost touches the display screen instead of or in addition to touching the stylus. So, some of the aforementioned national agencies also require that RFI/EMI fields emitted by a notepad computer while being operated by an operator be limited to levels that will not affect other equipment.
Besides the digitizer, the LCD panel, the electronic components on the computer system's processor board and the system cabling are sources for RFI/EMI fields that may be emitted through the display screen to the stylus and to the operator using the stylus. Unlike the digitizer RFI/EMI fields which are a side effect of the digitizing function, these RFI/EMI fields are completely spurious and have no useful purpose. Therefore, it is desirable to reduce these RFI/EMI fields as much as possible.
Personal communication devices have antennae that deliberately emit electromagnetic fields that are modulated in some manner to communicate information. Part of these emitted electromagnetic fields, typically, is radiated towards the personal communication device, its digitizer, its LCD panel and its electronic circuits. These electromagnetic fields that are not part of the communication channel can be a source of RFI/EMI fields that can interact with the digitizer, LCD panel, and personal communication electronic circuits and induce one or more single bit errors therein. Therefore, it is desirable to reduce the RFI/EMI fields that are radiated from an external antenna and are present at the internal circuits of a personal communication device.
It is an object of the present invention to provide a transparent, RFI/EMI shield apparatus that reduces the amount of RFI/EMI fields emitted by a combination of a notepad computer and an operator.
It is another object of the present invention to provide a RFI/EMI shield apparatus for a notepad computer that limits the RFI/EMI fields emitted by the notepad computer and yet allows a digitizer to sense the position of a stylus on its writing surface.
It is a further object of this invention to provide a transparent shield apparatus for a personal communicator device that reduces the RFI/EMI fields that are emitted at an antenna that reach the internal electronics of the personal communicator device.